摘要:

AbstractThe current range and relative abundance of the Egyptian MongooseHerpestes ichneumon(L.) in Portugal were studied using data obtained through direct field observations, personal communications and answers to enquiries. The present northern limit of its distribution has extended well beyond the Tagus River in most of its Portuguese range, indicating a probable expansion in recent years. A consistent increase in abundance was detected from north to south, latitude being highly correlated with computed indices of Mongoose abundance. The best‐fit model for predicting Mongoose relative abundance in the country considers latitude and human population density simultaneously. Altitude is the only environmental variable significantly correlated with the Mongoose abundance once the influence of latitude is discounted. Available information appears to indicate that the Portuguese Mongoose population is increasing, nevertheless research is needed in order to assess the impact of current predator control schemes on local population

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1996.tb00143.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractFive Striped Ground SquirrelsXerus erythropuswere radio‐tracked at Katumani, Kenya, for periods of up to 10 days. The results were used to explore their short‐term use of space. Definitions of the terms ‘home range’ and ‘core’, and some aspects of the methodology of home‐range analysis are discussed. In an area of low‐productivity bushland, subject to intermittent drought, where their food supply was patchy and unpredictable, the squirrels travelled about 1.5 km per day, and occupied rather large home ranges averaging 12.4 ha. Levels of aggression between conspecifics was low, home ranges were not defended, and there was considerable range overlap. Nights were spent in burrows which were commonly shared with conspecifics. On most days a single relatively long exploratory excursion was made outside the home range, extending the average area of the total range to some 40 ha. Despite the presence of major environmental features which might have been expected to affect the squirrels' foraging behaviour, such as cultivated fields, home range use was very symmetrical, suggesting that essential resources (food, shade, burrows) were widely dispersed throughout the range. Squirrels foraged alone, harvesting small, scattered, high‐quality food items, mainly vegetable. Activity was interrupted from time to time to retire to the shade to lose heat, and a midday rest was taken. Only part of the home range was used each day. A variable degree of central concentration of activity could be observed. The squirrels' use of space enabled them to exploit available food resources opportunistically and efficiently, and made them difficult to co

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1996.tb00144.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractExisting knowledge of the social organization, mating system and reproduction of Humpback Whales (Megaptera novaeangliae) is reviewed to assess how our current understanding of this wide‐ranging marine mammal fits into the predictive framework developed from ecological studies of more accessible terrestrial taxa. The small unstable groups characteristic of this species on its summer feeding grounds appear to be a function of absence of predation and of the patchy, mobile nature of most prey; the absence of territoriality and the minimal importance of kinship in associations are also predictable consequences of the latter. The mating system is similar to both leks and to male dominance polygyny, in which males display (sing) or directly compete (perhaps sometimes in coalitions) for access to females. However, the rigid spatial structure characteristic of classic leks is absent. The mating system of this species is sufficiently different to merit a novel category, and ‘floating lek’ is proposed. The widespread distribution of females resulting from absence of both predation and resources during the breeding season preclude simultaneous monopolization by males of more than one potential mate. Furthermore, these factors, together with a male‐biased operational sex ratio, minimize the possibility of competition among females. The intensity of intrasexual competition among males conforms to predictions derived from information on testis size and from expectation of future reproductive success. Female choice and, to a lesser extent, differential allocation of competitive effort by males, appears likely. Lack of interpopulation variation in social and mating behaviour, and in general reproductive biology, is likely a response to similarity of marine environmental conditions. Year‐to‐year variation in reproductive rates may be linked to variations in the abundance of prey. The invariably uniparous nature of female Humpback Whales is assumed to be related to the energetic demands of lactation, and the lower ratio of available energy partitioned to reproduction that is characteristic of larger mammals. The reversed sexual size dimorphism of this species may reflect different selective pressures on males and females. Finally, there is now evidence that, as in some other taxa, offspring sex ratio is related to materna

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1996.tb00145.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractFor much of the past two centuries, sperm whaling has been economically very profitable, and therefore whalers and, more recently, scientists have tried to understand Sperm Whale (Physeter macrocephalus) distribution and the factors controlling it. However, due to their deep‐living mode of life, their cosmopolitan distribution and our limited knowledge about their main prey species, the task has proved very difficult. This paper reviews studies of Sperm Whale distribution and the factors controlling it. The conclusions of these studies are very equivocal and often appear to contradict one another. It is suggested that this apparent confusion is mainly due to poorly defined spatial and temporal scales, the use of only one scale in most studies and the absence of consideration of the spatial and temporal scales at which relevant oceanographic processes occur. It is concluded that multiscale studies, covering the scales of oceanographic process, are needed to obtain a better understanding of Sperm Whale distributio

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1996.tb00146.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY